Technical Field
The present disclosure relates to a top-emission type electro-luminescence display apparatus capable of improving uniformity of brightness of the electro-luminescence display apparatus by reducing a degree of deviation of electric potential between anode and cathode according to the location of the respective pixels within the pixel area of the electro-luminescence display apparatus. The electro-luminescence display apparatus of the present disclosure is also capable of improving uniformity of electric potential when the electro-luminescence display apparatus is enlarged.
Discussion on the Related Art
An organic light emitting display apparatus, which is a self-luminous display device, does not require a separate or an additional light source, such as a liquid crystal display apparatus, and is therefore made in a light weight and thin form. In addition, the organic light emitting display apparatus is not only advantageous in terms of low power consumption due to its low driving voltage, but is also advantageous in terms of fast response speed, wide viewing angle and infinite contrast ratio.
The pixel area of an organic light emitting display apparatus includes a plurality of sub-pixels. Each of the sub-pixels includes an organic light emitting diode (OLED). Each of the organic light emitting diodes includes an anode which is a pixel electrode, an organic emission layer and a cathode which is a common electrode. An anode voltage ELVDD is supplied to the pixel electrode through a driving transistor and a cathode voltage ELVSS is supplied to the common electrode.
In a top-emission type organic light emitting display apparatus, reliability is required to protect the organic emission layer from, for example, oxygen and moisture. Thus, an encapsulation unit is formed to protect the organic emission layer from oxygen, moisture, physical shock and/or debris that may occur during a manufacturing process. The encapsulation unit may be chosen from a glass encapsulation unit, a transparent encapsulation unit in which an inorganic layer and an organic layer are alternatively stacked, or a dam and fill type transparent encapsulation unit in which an inorganic layer covers the organic light emitting diode on the first substrate, a transparent resin fills the area between the first substrate and the second substrate and a dam surrounds the transparent resin.
Further, in a top-emission type organic light emitting display apparatus, a semi-transparent (translucent) common electrode is a magnesium-silver (Mg:Ag) electrode, ytterbium (Yb) electrode and/or alloy thereof for releasing the emitted light at the organic emission layer toward the top side. To obtain the semi-transparent characteristic, the thickness of the common electrode can be very thin, for example, between 200 Å to 300 Å. However, in general, a reduction in thickness increases electrical resistance of the common electrode.
In a large sized top-emission type organic light emitting display apparatus, the electrical resistance of the common electrode tends to be high. Thus, a non-uniform brightness problem may arise if the distance from the cathode voltage supply unit, which can supply a cathode voltage ELVSS to the common electrode, increases.